Electrolytically deposited iron products



Patented Jan. 23, 1951 ELEGTROLYTIGALLY DEPOSITED IRON PRODUCTS HaroldV.-Trask, Cooley, Minn, 'assignor'to Buel' Metals company. Paul; Minn, acorporation of Ohio NoDraWin'g. Application-January 15,, 1947, SerialNo. 722,283

This invention relates 'to electrolytically deposited brittle iron plateand the powdersand colddie pressed hodi'e's formed from such plate.

The presentapplication is a continuation in part of my application forletters Patent of the United States-Serial No. 611,947, filed August 22,I945, which is a continuation-impart of my ap plication Serial No.560,783, file'd- October 28, 1 944, now abandoned;

The principal objects of my invention are:

1. To provide a low 'costiron deposit which is characterized by thepresence of a sufficient quantity of oxide and 'hydroxideof iron torender the product readily "grindable to particles-of. sizes suitablefor use in iron powder metallurgy and from which the hardeningconstituents may be readily removed bysimpleannealing. treatment.

2. To provide-ya. brittle iron plate which may be ground economically tominus 325 mesh :sizes and of such equiaxial-particleshapes-as to form inthe subsequent annealing treatment porous clusters of particles whichremain as porous clusters after the final crushing and screeningoperations.

3. To provide an electrolytically deposited, porous, brittle iron= platewhichadheres well to the cathodes during deposition.

4. To provide-aniron powder \vhiclrin structure and composition issuperior to the products of this kind heretofore produced Tonnes in colddie pressing operations.-

5. To provide an iron. powder which-is char acterized by its good flowrate, uniform screen size distribution, uniform apparent density and'high green strength when-compacted preparatory to sintering, combinedwith a high degree of purity, 'i. e.,;abovev 99.5

6. To provide an ironrpowder which is particularly adapted to receiveconventional cold die pressing and. sinteri-ng treatment to. form bodieshaving high tensile strength andv good elongation, dueto theuniformityof composition and improved grain. structure, substantially devoid ofplanes ofweakness.

7 To provide iron powders. having apparent densities which arecontrollable within narrow limits not exceeding 0.1 gram .per. cc.thereby affording uniformity in the compression ratio and greatlyfacilitating. standardized compacting operations.

8.. To provide iron powders .in. thefform of particles of controlledmesh sizes and off such purity, softness and structure that thecompacted' articles formed therefrom do. not expand appreciably orsubstantially when the pressure is removed preparatory'to sintering andalso of 2 such composition that the compacts do not shrinksubstantially-as a result of the sinteringtreatment.

Other objects wilillappe'ar' and be more fully pointed out. in thefollowing specification and claims.

My improved iron products may be electrodepos'ited' as described andclaimed in my applica'tion Serial No. 660,039, filed April 6,1946, or inaccordance with my application SerialNo. 611,947, filed August 22, I945,'he'reinbefore' referred to. In accordance with either process it isessential that the conditions present in the deposition cells withrespect to (1) solution composition, (2) current density of thedeposition and (3') temperature of deposition, shall be controlled andmaintained within the limits presently to be described. The range ofpermissible valuesfrom a technical standpoint" must be further limited;to minimize the'c'ost ofproduction and facilitate control in commercialoperations;

Solution composition An electrolyte comprising a ferrous chloridesolution has been found best suited for my purposes. The limits of thesolution concentration are: interrelated with those of the temperatureand current density of deposition. For example, the upper limit of ironconcentration, as ferrous chloride, in the solution is somewhatdependent on the lowest temperature which can be economi'callymaintained in the cell. If, as in most installations, it is noteconomical to keep the deposition temperature below 15 degrees C. themaximum concentration of. iron is approximately grams per liter for dullironplate deposition.

It is, however, much more economical to keep 7 the iron concentrationbelow this figure and I have found for most economical operation thatthe iron in solution should be maintained at between 50 and '75 gramsperliter. With more dilute solutions it is necessary to increase thevoltage inorder .to obtain a givencurrent density of deposition and thisprogressively increases the power consumed per pound ofiron depsited..It is feasible, however, to obtain dTullfiron plate with maximumsolution. concentrations ranging from about '67 to 86 grams of iron perliter where the currentdensities range from about 10 to 40' amperes persquare foot, and temperatures at or below 25 degrees C. are maintainedin the cells.

A further necessary control involves hydrogen ion concentration or thesolution. Its ,pl-I should 'be'ma'intainedbetween 3.0 "and 5.5. A pHlower than '3' indicates "the presence of excessive acid 3 or ferricchloride and results in a bright iron cathode deposit which is unsuitedfor my purposes and is otherwise not satisfactory because of its pooradherence to the cathode plates. In practice the pH of my solutionnaturally adjusts itself between 5 and 5.5. With pI-Is above 5.5 thesolution tends to hydrolyze and a deficiency of iron in solutiondevelops under conditions indicated by substantially higher pH values.solution is neither desirable nor necessary for the functioning of myprocess. Other additions to the electrolyte, such as ammonium chlorideand calcium chloride which have been used heretofore, are alsodetrimental.

The electrolyte for use in my process may be obtained by dissolvingscrap iron, preferably of low carbon content, in hydrochloric acid. Thisconcentrated solution of ferrous chloride is diluted so that it containsiron within the limits hereinbefore described and preferably about 60grams of iron, as ferrous chloride, per liter of solution.

Current density In order to produce my dull iron plate economically, thecurrent density between electrodes of the deposition cells must bemaintained between certain values which are interdependent upon theconcentration of iron in solution and temperature of deposition. Ingeneral, the higher the solution concentration the greater must be thecurrent density at any given temperature within the feasible range. Ashereinbefore indicated, practical limits of the current density are fromabout to 40 amperes per square foot where the solution concentrationranges from a maximum of about 67 to 87 grams of iron per liter ofsolution and where a temperature at or below 25 degrees C. is maintainedin the cell. The power consumed per pound of iron deposited increases indirect proportion to the current density and in inverse proportion tothe temperature of deposition.

Temperature of deposition In order to produce dull iron plate mosteconomically the temperature of deposition should be maintained betweendegrees and 35 degrees C. and preferably at approximately degrees C.where the economical ranges of current densities andsolutionconcentrations hereinbefore described are maintained. An unsatisfactory,bright, malleable deposit results when a temperature substantially above40 degrees C. is reached in a cell of the character described.

Cells and electrodes My process may be carried out in inexpensive opencells without diaphragms between the anodes and cathodes. In accordancewith my application Serial No. 650,039, ingot iron plates of suitablethickness, preferably about one-half inch thick, may be used as theelectrodes in the cells. These plates may contain up to 2% of carbon andsubstantial amounts of other impurities. For example, they may contain.03% carbon together with manganese, silicon and sulphur totalingapproximately .10 and copper approximately .15 Such electrodes areplaced in spaced, parallel, electrical series arrangement in the cellsand for maximum anode recovery are completely submerged in theelectrolyte. They are preferably spaced from two to three inches, centerto center, and furnished preferably in sizes that can be The presence offerric chloride in the 1 4 handled without the aid of power drivenhoists,

cranes or conveyors.

To control the temperature of deposition, inexpensive heat exchangersmay be placed in the cells or built into the walls of the same, or theelectrolyte may be circulated through a heat exchanger locatedexteriorly of the cells.

Direct current conductors are connected respectively to the endelectrodes of each cell and current is passed at the required voltagethrough the electrodes in series each of them constituting a solubleanode at one face and receiving a cathode deposit on its opposite face.t the start of the electrolysis, all electrodes are alike and they maycomprise ingot iron plates or other inexpensive iron plates containingimpurities as hereinbefore described. Either of the end electrodes mayact as a soluble anode and the other as a cathode depending on thedirection of flow of current.

During the electrolysis, the concentration of the electrolyte ismaintained as described and its pH tends to remain at its required valueof from 3 to 5.5. Periodically, if necessary, a small amount ofhydrochloric acid may be added. A cell temperature below 40 degrees C.maintained and current at the density required, preferably from 16 to 18amperes per square foot, is passed between electrodes in the seriesarrangement so that the metal from the positive face of each electrodegoes into solution and is re-deposited on the negative face of theelectrode adjacent to it. The electrolysis may be continued until all ithe electrodes have been converted into electro-deposited iron of thedesired dull gray and porous character. This product is subsequentlysubjected to the successive grinding, annealing, regrinding andscreening to produce my improved powders.

Further details of my series deposition process for forming dull ironplate are herein included by reference to my application Serial No.660,039.

As an alternative, the electrically parallel arrangement of electrodesin the cells, more fully described in my application Serial No. 611,947,may be employed. Accordingly, the electrodes may be providedindividually with leads extending to bus bars along opposite sides ofthe cell and the anodes may comprise ingot iron plates of suitablethickness, preferably from one-half to one inch thick and may contain upto 2% carbon and substantial amounts of other impurities. As thecathodes from which the dull iron plate may be removed periodically andwith ease, flexible cathode starting sheets comprising stainless steel,for example, that contains 18% chromium and 8% nickel may be used.Sheets of inch to inch thickness have been found to be adequately stifito remain straight in the cells while affording the flexibilitynecessary for removal of the brittle iron deposit. The electrolyte foruse in the parallel arrangement of anode and stainless steel cathodestarting sheets may be obtained by dissolving scrap iron as hereinbeforedescribed and may be diluted so that it contains iron within the limitsspecified and preferably between 50 and '75 grams of iron per liter. Thecells are cooled to maintain a temperature of electrolyte therein below40 degrees C. Where anode plates of approximately one inch thickness areused they may be spaced about two inches, center to center, relative tothe adjacent stainless steel cathode sheets. The current is supplied ata voltage such that there is a voltage drop between adjoining electrodeswithin the range 1.5 to 2 volts. Direct coatingis allowed to accumulatetoai-thickness of from%=to inch. The flexing-'of-theiron coatedsheetsmay be performed I manually by" bending thesheets oven a roller or bar,orotherwise in a" machine designed-for'the purpose; It maybe necessaryto' clean the cathodesheets periodically and this "may be accomplished"by dipping: them in dilute hydrochloricacidfor a period" of "fromone-tonve minutes: Cathode sheets of the character described areso'durable thatthey maybe used almost indefinitely. The anode plates aremerely replaced :by'new. ones periodically as they are'dissolvedinzthe'electrolyte. Other details of I the operation are well knowntinthis artand require no furtherrexplanation.

By maintaining: the-preferred conditions hereinbefore described in thecells, I obtain a porous, brittle, coherent; .dulliron deposit withcurrent efil'ciencies" above. 100 The reasons for this amazinglyhighefliciencyare notientirely clear. but'it is thought that itis; atleast in part due to the porosity and.- coherentnatureof mycathodedeposit.- The outer layer of iron as it is formed: may-.act-asanintermediate electrode between the anode plate and cathode sheet andelectrolysismaycause. decomposition of water in the pores between thisouterlayer and the cathode sheet' whereby hydrogen and oxygen areliberated inthese pores; Since the outer layer is iron in a: very pure.form itmay combinerwith .therliberated gases'to form iron .oxide. andhydroxide under theconditions existing in the cell. Accordingly, current efficiencies above. 100% may indicate that the iron is firstdeposited and later partially altered to the oxideand hydroxide statewithout affecting the carrying power of the current pass ing between theanode and cathode. Further substantiation of this theory may be found inthe fact that analyses of" the dull iron plate show that ironconstitutes only from 95% to 97.5% of theproductand that thehardening.contaminants areoxide and'hydroxidev compounds which can be easilyremoved-by annealing in. a hydrogen atmosphere.

My improved'iron is suffi'ciently brittle as deposited at the cathodeelectrodes to permit economical crushing or grinding and contains ironoxides and iron hydroxides together with a small amount-of chlorine,totaling approximately 3% to 5% of the deposit. This product has a darkgray color and is herein called dull iron plate. Otherphysical.characteristics of my dull iron plate are itsrhardness; diamond scale.ranging: from-. about; 400yto. 520; and its porositywhich gives it: aspecific: gravityranging; from apnroxi's' mately 6.3 to 7.25. Bycrushing or grinding-it: may be reduced to particles of the desired size(usually minus 100 mesh) and of equiaxial structure well adapted for usein iron powder metallurgy. Economical grinding to minus 325 mesh size isfeasible and advantageous for many uses. The dull iron plate may beground in a ball mill with air separation, or in any other suitableassays-92 grinder orpulverizer at low cost. It maybepul verizedto minus100' mesh sizes and with 50% or more of the particles of minus 325 meshsizes in a ball mill at the rate of 20 to" 25'poundsper 100 pounds ofballs per hour. Ordinary electrodeposited iron of comparable puritypulverizes at a rate of from 0.25 to 1.0 pound per 100 poundsof ballsper hour and cannot be pulverized to 'minus3251nesh sizes except atprohibitive cost. The hardening impurities, oxides and hydroxides, of mydull iron plate may be reduced and the resulting gaseous elementstogether with any chlorine carried over from the electrolyte may bedriven oh by simple annealing treatment leaving a product which is morethan 99.5% pure iron. Theannealing treatment preferably comprisesheating the ground product in a hydrogen atmosphere at approximately800' degrees'C. for from one to three hours, depending on the finenessof the product. Such annealing treatment causes substantial frittingwhich, in the case of particlesin the smaller ranges of sizes formsclustersadapted to withstand'the subsequentpulverizing and screening.After the second pulverizing and screening a controlled percentage ashigh as:%: of the final pure iron powder may compriseqpar ticlesbetween325 and 100 mesh sizes; ailarge pro:." portion of particles thereof*being'porous clusters? of smaller particles of substantially equiaxial;as distinguished from flat, shapes.

Analyses of a number of specimens: of' my dull 1 iron plate showthefollowing ranges of composi tion in percentages by weight:

. Per cent.

Total cathode iron -975- Cathode chlorine .3-.6: Weight loss afterheating: in nitrogen at 950 degrees C. for one'hour- 1.004155: Weightloss after heating in hydrogenat 950 degrees C. for one-hour 2.00-3.55

Total iron after reduction 99.5-99.9

By the annealing treatment in a hydrogen atmosphere, without previousheating in a nitrogen atmosphere, the weight loss amounts to from 3 to5% by weight.

Typical exampes of the physical'structure of" powders produced from suchdull iron plate are as follows:

Example 1 The dull iron plate was ground in a ball mill withairseparation to produce a powder all of which passed through a screenhaving openings per lineal inch and 75% of which, by-weight, passedthrough a screen or 325 mesh size. This powder-was then annea ed in ahydrogen atmosphere and maintained at a temperature" of ap-- proximately000 degrees C. for one and one-half hour; The resulting fritted mass,after cooling, was-pulverized in a hammer mill in closed circuit with ascreen of 100 mesh size. Numerous testsof the final powder showed thefollowing physical properties:

Flow rate, 50 grams through Hall flow meter, 30

to 33' seconds Screen analyses:

All minus 100 mesh 70% plus 325 mesh 30% minus 325 mesh Apparentdensity: 2.40 to 2.45 grams per cc. Apparent density variation: .05 gramper cc.

Example 2 Initial ball mill powder screen sizes, same as Example 1Annealing treatment: Same as Example 1 Screen analysis of final powder(after second grinding) All minus 80 mesh 80% plus 325 mesh 20% minus325 mesh Flow rate: 34 to 36' seconds Apparent density:2.l5 to 2.20grams per cc. Apparent density variation: .05 gram per cc.

Example 3 Initial ball mill powder screen sizes:

All minus 100 mesh 50% minus 325 mesh 50% plus 325 mesh Annealingtreatment: Same as Examples 1 and 2 Screen analyses of final powder:

All minus 80 mesh 80% plus 325 mesh 20% minus 325 mesh Flow rate: 30 to32 seconds Apparent density: 2.65 to 2.70 grams per cc. Apparent densityvariation: .05 gram per cc.

All tests show that the finished product fiows readily and hasremarkably uniform apparent density, since the apparent densityvariation for each example amounted to only .05 gram per cc. Moreover,the finished powders have unusually uniform screen size distribution.Microscopic examination shows further that the marked increase in grainsizes above 325 mesh in the final product as compared with the productof the first grinding treatment is due to the fritting of the finerparticles in clusters under the annealing temperature so that clustersof highly porous and substantially equiaxial structure form a majorfraction of the finished powder. Uniformity of apparent density is ofgreat importance since it is a major factor in imparting a uniformcompression ratio to the powder thereby greatly facilitating the coldcompacting operations. Since the second grinding does not reduce a largeproportion of the original particles to original size and form, theparticles are not reworked and hardened as in the case of ordinary ironpowders formed from bright iron plate. Consequentlymy final powder issofter and more amenable to compact pressures. Its good fiow propertyfurther facilitates the filling of intricate die cavities and promotesuniformly reliable results.

According to the present commercial practice in cold die pressingoperations, pressures within the range 30 to 100 tons per square inchare employed and my improved powder shows substantially no tendency toincrease in volume when such pressures are released from the compactedarticles. The green or unsintered strength of the compacted articles orbodies formed from my powder are sufiiciently high so that the articlesmay be handled and transferred from the cold dies to the sintering ovensreadily and without danger of breakage. Further, according to presentcommercial practice, green compacts are subjected to sinteringtemperatures of the order of magnitude of 1000 to 1100 degrees C. forperiods of from one to three hours, depending on the size of thecompact. Articles so sintered and comprising my improved powders showless than 8 0.5% shrinkage due to the sintering treatment and my testsindicate that the shrinkage usually ranges from .05 to 40%. The severaladvantageous properties described result in finished articles which areso accurately formed to dimension that machining is seldom required evenfor precision products.

Test bars comprising the powders of Examples 1, 2 and 3, hereinbeforedescribed, formed under 30 tons per square inch pressure and sinte'redfor one and one-half hours at 850 degrees C. have tensile strengthranging from 23,000 to 26,000 pounds per square inch and show elongationunder test equal to from 7% to 10% in one inch. Improved compaction aswell as unusually equiaxial grain structure and lack of planes ofweakness are evident from microscopic examination of polished: surfacesof the compacts. The pure iron powder may be mixed with other substancesto modify the properties of the end product.

Having described my invention, what I claim.

as new and desire to protect by Letters Patent is:

1. An electrolytically deposited, porous iron characterized by its dullgray color, hardness, diamond scale, 400 to 520; specific gravitybetween 6.3 and 7.25; weight loss after heating in nitrogen at 950degrees C. for one hour, 1.00 to 1.55%; weight loss after heating inhydrogen at 950 degrees C. for one hour, 2.00 to 3.55% and total ironafter reduction, above 99.5%.

2. An iron powder characterized by its dull gray color, specific gravitybetween 6.3 and 7.25; weight loss after heating in hydrogen at 950degrees C. for one hour, 3.0 to 5.0%, all particles being of mesh andsmaller sizes and a major fraction of the particles by weight being ofminus 325 mesh sizes and of substantially equiaxed shape.

3. An electrolytically deposited iron characterized by its specificgravity between 6.3 and 7.25; hardness, diamond scale, 400 to 520; thehardening impurities comprising oxide and hydroxide compounds which arereadily removable by annealing, and the purity after reduction beingabove 99.5%.

HAROLD V. TRASK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Hardy et a1 May 9, 1939 Whitfield et a1Dec. 3, 194:0 Bauer June 23, 1942 Young Sept. 22, 1942 Talmadge June 29,1943.

FOREIGN PATENTS Country Date Germany Dec. 5', 1949 OTHER REFERENCES Numer Number

1. AN ELECTROLYTICALLY DEPOSITED, POROUS IRON CHARACTERIZED BY ITS DULLGRAY COLOR, HARDNESS, DIAMOND SCALE, 400 TO 520; SPECIFIC GRAVITYBETWEEN 6.3 AND 7.25; WEIGHT LOSS AFTER HEATING IN NITROGEN AT 950DEGREES C. FOR ONE HOUR, 1.00 TO 1.55,; WEIGHT LOSS AFTER HEATING INHYDROGEN AT 950 IRON AFTER REDUCTION, ABOVE 99.5%.